1. Technical Field
The present invention relates to an electrophoretic device and electronic equipment having the electrophoretic device as a-display.
2. Related Art
An electrophoretic device having a pair of electrodes and an electrophoretic dispersion liquid that includes a liquid dispersion medium and electrophoretic particles interposed between the pair of the electrodes has been known. The electrophoretic device can display desired information by controlling amplitude, polarity, waveform and frequency of a voltage applied to the pair of the electrodes and a time period to apply the voltage.
There is a type of the electrophoretic device in which the electrophoretic dispersion liquid is enclosed in a microcapsule in order to stabilize the motion of the electrophoretic particles. A dispersion liquid that consists of a dispersion medium colored with dyes and a more than one kind of the electrophoretic particles dispersed in the dispersion medium is enclosed in the microcapsule. JP-A-64-86116 is a first example of related art. This microcapsule type electrophoretic device has a binder layer that contains the microcapsules and is interposed between a pair of electrodes. Here, one of the electrodes is made transparent. The electrophoretic particles in the microcapsules move according to the polarity of the voltage applied to the electrodes. This property of the electrophoretic device can be used as a display.
JP-A-2004-4714 is a second example of related art. As electronic equipment, a display using the microcapsule type electrophoretic device driven by thin film transistors has also been known.
In the case that the electrophoretic device is used as a display, the electrophoretic particles generally remain at the same position and the display image can be retained even when the voltage application to the electrodes is stopped.
However, in the case of the microcapsule type electrophoretic device, a transient phenomenon occurs at the moment that the voltage application to the electrodes is stopped because of the electric charge stored in the electrophoretic device. At this point, the electric field with the opposite polarity to that of the electric field heretofore applied to the electric charge is temporary impressed upon the electrophoretic particles in the microcapsule. Accordingly, a part of the electrophoretic particles that are regularly retained in the microcapsule corresponding to the polarity (+/−) of the electrodes is moved toward the electrode having the opposite polarity. In other words, the contrast of letters and the like shown on the display is deteriorated compared to the case when the voltage is applied to the electrodes because the part of the electrophoretic particles is moved.
If the electronic equipment has such electrophoretic device as a display (display means), the credibility of the image quality cannot be ensured.